Platform: properly include SDL_main.h for iOS.

Got missed when cleaning up the 50kLOC header mess in
b73b9cb408 (Nov 2018). Sorry!

doc/changelog.dox

@@ -177,6 +177,11 @@ See also:
 -   Fixed broken @ref Platform::EmscriptenApplication mouse event coordinates
     when `-s DISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=1` is enabled (see
     [mosra/magnum#408](https://github.com/mosra/magnum/issues/408))
+-   In 2019.01 @ref Magnum/Platform/Sdl2Application.h went through an include
+    cleanup, removing 50k lines; but unfortunately we forgot to add back
+    @cpp #include <SDL_main.h> @ce, causing iOS builds to fail to initialize.
+    The include got added back and initialization failures are reported with
+    more information now.
 
 @subsection changelog-latest-deprecated Deprecated APIs
 

doc/snippets/MagnumGL-framebuffer.cpp

@@ -97,4 +97,5 @@ GL::Buffer b; // implicitly tied to `other`
 /* [Context-makeCurrent] */
 }
 
+return 0; /* on iOS SDL redefines main to SDL_main and then return is needed */
 }

src/Magnum/Platform/Sdl2Application.h

@@ -61,6 +61,16 @@
 #include <SDL_video.h>
 #include <SDL_scancode.h>
 
+#ifdef CORRADE_TARGET_IOS
+/* Including SDL_main.h unconditionally would mean it'd override Corrade::Main
+   on Windows (both are parsing wargv and converting them to UTF-8, but ours
+   does that better and additionally enables ANSI colors and UTF-8 console
+   output). Right now (SDL 2.0.11) it's only needed for WinRT (which is done
+   below), Android (which we don't support for SDL) and iOS, so whitelist it
+   only for iOS. */
+#include <SDL_main.h>
+#endif
+
 #ifdef CORRADE_TARGET_WINDOWS_RT
 #include <SDL_main.h> /* For SDL_WinRTRunApp */
 #include <wrl.h> /* For the WinMain entrypoint */